The present invention relates to a master cylinder for supplying a brake fluid to a brake system of an automobile or the like.
A master cylinder has a cylinder member in the shape of a cylinder, one end of which is closed, and a piston inserted in the cylinder member to form a pressure chamber in the cylinder member. The piston reduces the volume of the pressure chamber according to the amount of depression of the associated brake pedal, thereby supplying the brake fluid from the pressure chamber to the brake system.
In such a master cylinder, for example, a port is formed in the cylinder member to provide communication between the pressure chamber and a reservoir for storing the brake fluid to supply the brake fluid into the pressure chamber. It is necessary in order to supply the brake fluid smoothly to ensure a sufficient fluid passage sectional area for the port. Conventionally, the port is formed by boring and has a circular sectional configuration. Therefore, in order to ensure a sufficient fluid passage sectional area for such a port having a circular sectional configuration, the diameter of the port needs to be enlarged. However, there are limits to ensuring a sufficient fluid passage sectional area simply by increasing the port diameter because of the relationship with other constituent parts. It has been contrived to ensure a sufficient fluid passage sectional area by providing a plurality of circumferentially spaced holes in the cylinder member. However, this method needs to perform a boring process a plurality of times and hence requires an increased number of man-hours for processing, resulting in an increase in cost.
An object of the present invention is to provide a master cylinder capable of being produced with a reduced number of man-hours and hence at reduced cost and still capable of ensuring a sufficient fluid passage sectional area for the port.